The present invention relates to techniques for time certification for digital data.
Conventionally, a time stamp technique has been available in which each user transmits digital data for which time is desired to be certified to a TSA (Time-stamping Authority) and the TSA generates time certification information (called a time stamp) on the basis of the digital data and time information at that point of time.
The conventional time stamp technique is detailed in a literature [AC] “Applied Cryptography Second Edition” by Bruce Schneier, John Wiley & Sons, Inc., 1996.
A method has also been available which utilizes, as the time certification information generated by the TSA, a digital signature, based on a secrete key by the TSA, for digital data received from a user and time information at a time point of time stamp issuance.
The time certified by the generated time stamp according to the prior arts as above corresponds to a point of time at which the TSA carries out a time stamp generating process and which is later than a time requested by the user. Especially when requests for time stamp generation are made concentrically to the TSA from many users within a short period of time, the delay is more aggravated or further increased. Also, in the event that the TSA fails to proceed with processing for some reasons, the user cannot obtain time certification for the digital data.
With electronic commerce transacted briskly and widely, a demand for a time stamp increases and the advent of an improved time stamp method or system has been desired.